Certain espresso beverages are known to be obtained by brewing or instantaneous extraction of flavors and active ingredients of more or less edible products, such as coffee, barley, malt, ginseng, infusions and other similar products in powder or particle form, using warm or hot water at ambient pressure or preferably at a pressure above the atmospheric pressure.
As used herein, the term espresso is intended to designate a beverage that is prepared instantaneously or for a waiting consumer.
A particular class of base products requires grinding to obtain products of various particle sizes.
A typical, non-exclusive example of such class of products is coffee, which is previously mixed, roasted and then cold-ground to obtain the classical coffee grounds that are sold in hermetically and vacuum sealed packages for home and public use.
In order to prepare an espresso coffee, a given amount of coffee grounds is loaded in a perforated container, known as filter container, whereupon the loaded grounds are compressed manually or using a special tamper.
Then, hot water is forced through the compressed grounds are at a given pressure, using a special machine.
A high-quality espresso coffee, as typically requested in bars, requires some skill and a high-cost professional machine.
For domestic preparation of high-quality espresso coffee, portions of coffee grounds have been long available, which are pre-packaged as pods made of filter paper or plastic capsules of various shapes and sizes. These items are introduced into relatively inexpensive machines, which are affordable to private consumers or small-size businesses and communities, to prepare a top-quality espresso.
Examples of these pre-packaged items are disclosed, for instance, in FR 1 029 940, U.S. Pat. Nos. 1,951,357, 4,394,395, IT 1 213 385.
One drawback of such prior art methods and items for preparing espresso coffee consists in the relatively high costs for manufacturing and packaging capsules or pods, which results in accordingly high sales costs for the final consumer.
A further drawback is that this known type of packaging requires the presence of enclosures made of plastic, paper, aluminum or other materials to contain the products to be filtered, which make the manufacturing process more complex and problematic.
Yet another drawback relates to environment-friendly disposal and environmental impact reduction issues, due to such enclosures, after coffee dispensing.
In an attempt to obviate the above drawbacks, a novel process has been developed for producing tablets or pastilles, that does not require any kind of enclosure, but requires moistening of the tablet and application of energy thereto, in the form of vibrations, namely high-frequency ultrasonic vibrations.
Processes of this type are disclosed and claimed, for instance, in EP1956921 e WO2001/027426.
While this novel preparation method has provided a number of advantages over prior art products, such as the elimination of the plastic enclosure for coffee grounds, which considerably reduces environmental impact, it still has the drawback that vibrations are required to be transferred by contact or through an interposed medium, which increases the complexity and costs of the manufacturing process.
Furthermore, the tablet is not uniformly compacted, as ultrasonic waves are progressively attenuated as they pass through the tablet, and the tablet cannot be compacted above a given thickness limit.